Supercritical fluid chromatography hyphenated techniques

Jinno, K., Hyphenated Techniques in Supercritical Fluid Chromatography and Extraction, Elsevier, Amsterdam, 1992. 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instmments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance Hquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instmments such as gc/ftir are often termed hyphenated instmments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instmmentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

H.H. Hill and D.A. Atkinson, in Hyphenated Techniques in Supercritical Fluid Chromatography and Extraction (K. Jinno, ed.), Elsevier, Amsterdam (1992), pp. 1-8. 

Figure 7.16 Schematic representation of off-line SFC-FTIR. After deposition of the eluites on to a moving ZnSe substrate the window is moved to the focus of a stand-alone FTIR microscope, where the spectmm of each spot is measured with the plate stationary. After Griffiths et al. [374]. Reprinted from P.R. Griffiths et al., in Hyphenated Techniques in Supercritical Fluid Chromatography and Extraction (K. Jinno, ed.), pp. 83-101, Copyright (1992), with permission from Elsevier...

This article treats the benefits, possibilities and drawbacks of supercritical fluid chromatography (SFC) and supercritical fluid extraction (SFE) coupled to nuclear magnetic resonance spectroscopy. After a general overview and consideration of the motivation for such techniques, the design of high-pressure flow probes, as well as the principle experimental set-ups, are described. By means of several applications and comparison to HPLC-NMR, the utility of these hyphenated techniques is demonstrated. 

While supercritical fluid chromatography seems to have a controversial benefit, supercritical fluid extraction (SFE) is a technique used world-wide and plays an important role in many industrial processes, such as the decaffei-nation of coffee. Due to the high information content of NMR spectroscopy, the hyphenation of SFE with NMR spectroscopy promises a deep insight into the extraction process itself, thus leading to a better understanding and development of more efficient extractions. 

The first exposure to spectroscopy for most scientists is ultraviolet/ visible absorbance. As virtually every HPLC chromatograph employed in the pharmaceutical industry uses UV absorbance as the detection method, it is no wonder that the most popular hyphenated technique is HPLC-DAD. DAD spectrographs have been coupled to all liquid-based chromatographic systems including HPLC (preparative, analytical, and microbore), capillary electrophoresis (CE) and supercritical fluid chromatography (SFC). There have been several successes with TLC plates,18 but it is more common for developed plates to be scraped and the sample analyzed offline. 

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